The present invention relates to a field-emission type display and a projection tube, which are equipped with a faceplate where a phosphor layer is formed, and means for irradiating electron beams to the phosphor layer. The present invention more specifically relates to such a field-emission display (hereinafter, referred to as an xe2x80x9cFEDxe2x80x9d) and such a projection tube, into which small particle phosphors have been mixed, which constitutes the phosphor layer.
In picture information systems, various sorts of display apparatus have been positively researched and/or developed in order to satisfy various requirements, for example, high resolution, large screen sizes, thin type displays, and low power consumption. Display apparatus with employment of Braun tubes have been widely utilized in present fields. However, there are limitations in requirements as to thin type Braun tubes. To realize such thin type displays and low power consumption, FED has been very recently researched/developed in order to satisfy these requirements.
FED has a structure such that a plane-shaped field-emission type electron source is mounted on a rear plane of enclosed a vacuum box, and phosphor layers are provided on inner surfaces of faceplates of front planes thereof. In the FED, while an electron beam of low accelerating voltage (on the order of approximately 0.1 to 10 kV) are irradiated to the phosphor layers so as to emit light therefrom, an image is displayed on the FED. In this case, since electron density of the electron beam irradiated to the phosphor layer is approximately 10 to 1000 times higher than the electron density of the general-purpose Braun tube, namely high electron density, low resistance characteristics are required for the phosphor layer used in the FED, under which the phosphor layers are not saturated with electric charges. Furthermore, better lifetime characteristics under high electron density are required, and also, high luminescent characteristics with less luminescent saturation are required.
Also, there is another problem. That is, since the electron beam is irradiated onto the phosphor layer in high electron density, the electron beam may pass through the phosphor layer and then may be reached to an inner plane of faceplate, which may induce browning glass to change colors of the glass into brown colors. As a result, luminescent lifetimes of displays are lowered. Also, this browning glass phenomenon may constitute one of factors capable of lowering luminescent lifetime as to the projection tube. Generally speaking, in such a projection tube, the electron beam irradiated onto a phosphor layer in high electron density, which is approximately 100 times higher than that of a general-purpose Braun tube. This luminescent lifetime aspect of the projection tube should be solved.
Various development has been so far carried out in order to realize low resistance characteristics of phosphor layers, long lifetime characteristics thereof, and high luminescent characteristics thereof. As a method capable of improving performance of the phosphor layers used for FED by mixing the phosphors with the phosphor layers, for instance, JP-A-9-87618 describes such a method that since the high resistance phosphors are mixed with the low resistance phosphors, the superior luminescence characteristics may be owned under such a drive voltage lower than, or equal to 2 kV. Also, for example, JP-A-12-96046 discloses such a method that while the mixed phosphors are constituted by both the sulfur-system phosphors, and the oxide-system phosphors corresponding to either the aluminum oxide system of yttrium or the silicate system, the luminescent maintenance factor may be kept better over a long time duration.
On the other hand, although not being used in FED fields, as a method of mixing phosphors having different particle diameters with each other, JP-A-7-245062 describes the following method. That is, in the plasma display apparatus, the unnecessary discharge which is caused by exposing the address electrode may be suppressed by the phosphor layer having the fine structure in which the blue-color phosphors having the small particles are entered into the blue-color phosphors having the large particles.
Various sorts of methods have been studied in order to realize the low resistance, the long lifetime, and the high luminescence as to the phosphor layers used in FED. However, these conventional methods could not solve all of these problems. More specifically, such a novel method is necessarily required, by which not only resistances of the respective phosphors, but also the resistance of the entire phosphor can be lowered. Also, this novel method can realize the long lifetime as well as the high luminescence of the phosphor layers, and further, can mitigate the browning glass phenomenon.
As a consequence, an object of the present invention is to improve the respective low resistance characteristics, lifetime characteristics, and also luminescent characteristics of the above-explained conventional phosphor layer, and furthermore, is to provide both a field-emission display and a projection tube, which may have superior characteristics by reducing browning glass.
The above-described object may be achieved by that in a field-emission display equipped with a faceplate on which a phosphor layer is formed, and means for irradiating electron beam onto the phosphor layer, an image display apparatus is featured by that the phosphor layer is constituted by phosphors formed by mixing main phosphors with small particle phosphors, the averaged particle diameter of which is smaller than xc2xd of an averaged particle diameter of the main phosphors. In other words, one of the features of the phosphor layers used in the image display apparatus is given as follows. That is, since the small particle phosphors are mixed with the main phosphors, the small particle phosphors are entered into the spaces of the main phosphors, and the contacts occurred among the phosphors are increased, so that the lower resistance of the entire phosphor layer can be realized.
Also, in the case that an average particle diameter xe2x80x9cBxe2x80x9d of small particle phosphors is expressed by 0.16Axe2x89xa6Bxe2x89xa60.28A, which are mixed with main phosphors having an averaged particle diameter xe2x80x9cAxe2x80x9d, the small particle phosphors are just entered into the spaces of the main phosphors, so that the filling density of the phosphor layer may be improved. Furthermore, in the case that the small particle phosphors are mixed with respect to the main phosphors in 2 weight % to 50 weight %, the small particle phosphors are entered into the spaces of the main phosphors, so that the filling density of the phosphor layer may be improved.
Also, when the phosphor layer is constituted by phosphors formed by mixing main phosphors, the averaged particle diameter of which is expressed by xe2x80x9cAxe2x80x9d, with small particle phosphors, in such a case that the averaged particle diameter of which is expressed by xe2x80x9cBxe2x80x9d, a volume of a position of the averaged particle diameter xe2x80x9cBxe2x80x9d is larger than a normal distribution curve by 2 weight % to 50 weight %, and the small particle phosphors are entered into the spaces of the main phosphors, so that the filling density of the phosphors layer can be improved. Furthermore, in the case that a volume of a position of the averaged particle diameter xe2x80x9cBxe2x80x9d is larger than the normal distribution curve by 6 weight % to 12 weight %, the filling density of the phosphor layer can be furthermore improved.
Also, since components of the main phosphors are identical to components of the small particle phosphors mixed with the main phosphors, the low resistance of the phosphor layer can be realized without changing the light emitting characteristic of the phosphors.
Also, since the main phosphors are ZnS:Ag phosphors corresponding to sulfur-system phosphors, and the phosphors to be mixed thereto are any one sort, or plural sorts of the below-mentioned phosphors: Y2SiO5 Ce, (Y,Gd)2SiO5; Ce, ZnGa2O4, CaMg Si2O6:Eu, Sr3MgSi2O8:Eu, Sr5(PO4)3Cl:Eu, YNbO4; Bi, corresponding to oxide-system phosphors, scattering of sulfur can be reduced. While the resistance of the phosphor larger can be lowered, the lifetime characteristic and the luminescent characteristic can be improved, so that the better blue-color phosphor layer used in the FED can be realized.
Also, since the main phosphors are Y2O2S:Eu phosphors corresponding to sulfur-system phosphors, and the phosphors to be mixed thereto are any one sort, or plural sorts of the below-mentioned phosphors: Y2O3 Eu, SrTiO3:Pr, SnO2:Eu, SrIn2O4:Pr, corresponding to oxide-system phosphors, scattering of sulfur can be reduced. While the resistance of the phosphor layer can be lowered, the lifetime characteristic and the luminescent characteristic can be improved, so that the better red-color phosphor layer used in the FED can be realized.
Also, since the main phosphors are any one sort, or plural sorts of the below-mentioned phosphors: Y2SiO5:Tb, (Y,Gd)2SiO5:Tb, Y3(Al,Ga)5O12; Tb, (Y,Gd)3(A,Ga)5O12; Tb, ZnGa2O4:Mn, Zn(Ga,Al)2O4:Mn, ZnO:Zn, corresponding to oxide-system phosphors, and also the small particle phosphors mixed with the main phosphors are any one sort, or plural sorts of the below-mentioned phosphors: ZnS:Cu, ZnS:Cu,Au, corresponding to sulfur-system phosphors, the contacts occurred among the respective phosphors are increased. While the resistance of the phosphor layer can be lowered, the lifetime characteristic and the luminescent characteristic can be improved, so that the better-green-color phosphor layer used in the FED can be realized.
Also, since the main phosphors are any one sort, or plural sorts of the below-mentioned phosphors: Y2O3:Eu, SrTiO3:Pr, corresponding to oxide-system phosphors and also the small particle phosphors mixed with the main phosphors are Y2O2S:Eu phosphors, corresponding to sulfur-system phosphors, the contacts occurred among the respective phosphors are increased. As a result, while the resistance of the phosphors layer can be lowered, the lifetime characteristic and the luminescent characteristic can be improved, so that the better red-color phosphor layer used in the FED can be realized. Furthermore, the above-described object may be achieved by such a projection tube. That is, in a projection tube equipped with a faceplate on which a phosphor layer is formed, and means for irradiating electron beams onto the phosphor layer, the projection tube is provided with such a phosphor layer in which the phosphor layer is formed by mixing small particle phosphors into main phosphors in a range larger than, or equal to 5 weight %, and also smaller than, or equal to 70 weight %, while an averaged particle diameter of the small particle phosphors is small with respect to the main phosphors. In other words, as one of the features of the phosphor layer employed in the image display apparatus according to the present invention, since the small particle phosphors are mixed with the main phosphors, the small particle phosphors are entered into the spaces of the main phosphors, so that the filling density of the phosphor layer can be improved.
Also, since the small particle phosphors are entered into the spaces of the main phosphors, the contacts occurred among the phosphors are increased, so that the low resistance of the entire phosphor layer can be realized.
Also, such a phosphor layer is employed, in which the phosphor layer is formed by mixing the small particle phosphors into the main phosphors in a range larger than, or equal to 10 weight %, and also smaller than, or equal to 40 weight %, while an averaged particle diameter of the small particle phosphors is small with respect to the main phosphors. As a result, the filling density of the phosphor layer can be improved.
Since the above-described phosphor layer having such features is employed, while the browning glass caused by the irradiation of the electron beams which have passed through the inner plane of the faceplate can be improved in the projection tube and the field-emission type display, the image display apparatus having the better luminescent lifetime can be provided.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.